On 09/05/2014 09:03 AM, Badari Rao wrote:
I have collected EXAFS data on a ferroelectric perovskite Sodium Bismuth Titanate which has an average rhombohedral R3c structure and am trying to fit the data with R3c as the starting model. But I am having trouble in implementing constraints for the fit. I found a paper authored by you, titled "Local structrue and phase transitions of BaTiO3, Ferroelectrics, 1998, 206-207, pp 407-430". I want to do similar kind of analysis using Artemis on my data. However, I am finding difficulty in understanding how the constraints have been implemented for the refinement of the barium K edge EXAFS, especially those for the bond lengths (Page 416 in the above mentioned article in particular is unclear). Could you please explain how the GDS window and the variables for different paths in this case would look like. Also how do you decide what parameters to refine and what to keep fixed (table IV in the article)?
Also can you please suggest some literature for beginners which can guide me in implementing such constraints?
Badari, You are asking a very broad and open ended question. Since you self-identify as a beginner, I would recommend spending some time learning the basics of XAS and XAS analysis. You could start by reading one of the recent text books on XAS by Grant Bunker or Scott Calvin: http://www.amazon.com/Introduction-XAFS-Practical-Absorption-Spectroscopy/dp... http://www.amazon.com/XAFS-Everyone-Scott-Calvin/dp/1439878633 To learn about the practice of XAS, there are links to tutorials at http://xafs.org/Tutorials Shelly Kelly's tutorials specifically address the use of Athena and Artemis. To learn about the use of my software, there are links to a lot of information, including links to videos of me demonstrating their use, at the Demeter website: http://bruceravel.github.io/demeter/ To learn specifically about the application of constraints to EXAFS analysis, two excellent papers with extensive discussions of how to apply sophisticated constraints are: http://dx.doi.org/10.1103/PhysRevB.66.224405 http://dx.doi.org/10.1016/S0016-7037(02)00947-X While neither of those papers are on the topic of titanate perovskites, you would do well to read them carefully and understand the analysis strategies that Scott or Shelly describe. HTH, B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://bruceravel.github.io/home/ Software: https://github.com/bruceravel Demeter: http://bruceravel.github.io/demeter/